In a semiconductor manufacturing process, a flow rate control apparatus which is known as a mass flow controller and in which are packaged various types of fluid instruments and control mechanisms is used in order to control flow rates of various types of gases that are introduced, for example, into an etching chamber.
A mass flow controller is provided, for example, with a flow rate sensor that is provided on a flow path, a valve that is provided on a downstream side of the flow rate sensor, and a flow rate control part that controls an valve opening of the valve such that a measured flow rate that is measured by the flow rate sensor matches a set flow rate which is a target value (see Patent Document 1).
In a mass flow controller such as this, because the measurement point of the flow rate sensor and the control point of the valve on the flow path are mutually separated by the distance between the locations where the respective devices are installed, a delay is generated in the control, particularly in the case of a transient response.
In order to solve this type of problem, attempts have been made to eliminate the delay in the control by estimating the valve flow rate actually flowing at the control point, and then feeding back this estimated valve flow rate. More specifically, a pressure within a volumetric space between the flow rate sensor and the valve is measured by a pressure sensor, and the valve flow rate, which is the flow rate at the control point, is estimated from differential values of this pressure and the flow rate measured by the flow rate sensor.
However, if a differential operation is performed when, for example, high frequency noise is present in the pressure measured by the pressure sensor, then a greater level of noise also becomes attached to the estimated valve flow rate. If a valve flow rate that contains a large noise component such as this is then fed back, there is a possibility that the control of the valve will become unstable.